I’d like a convenience extension to return true when a nullable string is not null, and not blank — ...

# getting-started

[andym]

I’d like a convenience extension to return true when a nullable string is not null, and not blank — neither should be processed.
After the extension returns true for an immutable, I don’t want to have to have to !! it.
But it seems I can’t use “this” in a contract:

contract {
        returns(true) implies (this != null)
    }

    return !this.isNullOrBlank()

Is there a way to do this?

[Youssef Shoaib [MOD]]

you need to use a qualified this instead, and so assuming your function is called myCastAsNullOrBlankFun, then your contract should be this:

contract {
    returns(true) implies (this@myCastASNullOrBlankFun != null)
}

[Nicolas B]

Why you use a contrat ?

[Nicolas B]

fun String.checkNotNull(): Boolean{
    return !isNullOrBlank()
}

[ephemient]

fun String.isNullOrBlank() itself has a contract,

contract {
    returns(false) implies (this@isNullOrBlank != null)
}

[ephemient]

not clear why you would need another function to wrap it, but for sure the this you wrote is not referring to what you think it is - it's this@contract

[andym]

@Youssef Shoaib [MOD] perfect, thanks!

[andym]

@Nicolas B, I would prefer a contract so that after I prove my immutable value is not null, I don’t need !!, or anything else — I just want a custom smart-cast to non-nullable